A generic longitudinal adjuster and a generic vehicle seat are disclosed in DE 10 2011 011 766 A1. The longitudinal adjuster comprises two rail pairs with in each case two seat rails which are displaceable relative to one another, namely an upper rail and a lower rail which mutually encompass one another. The upper rail is able to be displaced relative to the lower rail within a comfort adjustment region and moreover into an easy entry position.
Bearing elements are provided between the upper rail and the lower rail, said bearing elements preferably comprising ball cages consisting of plastics material and metal balls rotatably mounted therein. The ball cages in this case are arranged in the intermediate spaces between the upper rail and the lower rail, wherein the balls are in contact with the upper rail and with the lower rail. During a displacement of the upper rail relative to the lower rail, the balls roll thereon.
The spacing of the first ball relative to the last ball of the ball cage defines the support length between the upper rail and the lower rail. The first ball and the last ball are generally arranged in the vicinity of the ends of the ball cage. Thus, the length of the ball cage approximately corresponds to the support length between the upper rail and the lower rail. The greater the support length, the greater the rigidity of the longitudinal adjuster.
With a displacement of the upper rail relative to the lower rail by a predetermined adjustment path, the ball cages move precisely by half of this adjustment path. The maximum possible length of the ball cages is thus defined by the length of the upper rail and the lower rail and by the maximum adjustment path. As a result, the support length and the rigidity of the longitudinal adjuster are also limited.
A high degree of rigidity of the longitudinal adjuster also causes a high natural frequency of the vehicle seat. Here, the highest possible natural frequency of the vehicle seat is desirable, so that low frequency excitations through the chassis of the vehicle which are transmitted to the vehicle seat do not lead to a build-up and thus to troublesome noises or vibrations. The noises may occur primarily with an empty vehicle seat, i.e. not occupied by an occupant.
A longitudinal adjuster for a vehicle seat is disclosed in DE 20 2006 016 652 U1 and which, on the one hand, comprises rotatable balls arranged between the upper rail and the lower rail and, on the other hand, cylindrical rollers mounted on the lower rail.
A longitudinal adjuster for a vehicle seat is disclosed in EP 0 067 123 A1 and which also comprises rotatable balls arranged between the upper rail and the lower rail and additionally cylindrical guide rollers which are rotatable about an axis extending in the transverse direction.
A roller guide for a vehicle seat is disclosed in DE 10 2004 038 507 A1. The roller guide comprises a guide roller which is rotatably mounted about an axis extending in the transverse direction, said guide roller rolling on a guide rail.